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Date: Wed, 13 Mar 2013 10:33:57 -0500
From: Seth Jennings <sjenning@...ux.vnet.ibm.com>
To: Dan Magenheimer <dan.magenheimer@...cle.com>, minchan@...nel.org,
Nitin Gupta <nitingupta910@...il.com>,
Konrad Wilk <konrad.wilk@...cle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Bob Liu <lliubbo@...il.com>,
Luigi Semenzato <semenzato@...gle.com>,
Mel Gorman <mgorman@...e.de>
Subject: Re: zsmalloc limitations and related topics
The periodic writeback that Rob mentions would go something like this
for zswap:
---
mm/filemap.c | 3 +--
mm/zswap.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 59 insertions(+), 7 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..fe63e95 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -735,12 +735,11 @@ repeat:
if (page && !radix_tree_exception(page)) {
lock_page(page);
/* Has the page been truncated? */
- if (unlikely(page->mapping != mapping)) {
+ if (unlikely(page_mapping(page) != mapping)) {
unlock_page(page);
page_cache_release(page);
goto repeat;
}
- VM_BUG_ON(page->index != offset);
}
return page;
}
diff --git a/mm/zswap.c b/mm/zswap.c
index 82b8d59..0b2351e 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -42,6 +42,9 @@
#include <linux/writeback.h>
#include <linux/pagemap.h>
+#include <linux/workqueue.h>
+#include <linux/time.h>
+
/*********************************
* statistics
**********************************/
@@ -102,6 +105,23 @@ module_param_named(max_compression_ratio,
*/
#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
+/*
+ * The amount of time in seconds for zswap is considered "idle" and periodic
+ * writeback begins
+ */
+static int zswap_pwb_idle_secs = 30;
+
+/*
+ * The delay between iterations of periodic writeback
+ */
+static unsigned long zswap_pwb_delay_secs = 1;
+
+/*
+ * The number of pages to attempt to writeback on each iteration of the periodic
+ * writeback thread
+ */
+static int zswap_pwb_writeback_pages = 32;
+
/*********************************
* compression functions
**********************************/
@@ -199,6 +219,7 @@ struct zswap_entry {
* The tree lock in the zswap_tree struct protects a few things:
* - the rbtree
* - the lru list
+ * - starting/modifying the pwb_work timer
* - the refcount field of each entry in the tree
*/
struct zswap_tree {
@@ -207,6 +228,7 @@ struct zswap_tree {
spinlock_t lock;
struct zs_pool *pool;
unsigned type;
+ struct delayed_work pwb_work;
};
static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
@@ -492,7 +514,7 @@ static int zswap_get_swap_cache_page(swp_entry_t entry,
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics.
*/
- found_page = find_get_page(&swapper_space, entry.val);
+ found_page = find_lock_page(&swapper_space, entry.val);
if (found_page)
break;
@@ -588,9 +610,8 @@ static int zswap_writeback_entry(struct zswap_tree *tree, struct zswap_entry *en
break; /* not reached */
case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */
- /* page is already in the swap cache, ignore for now */
- return -EEXIST;
- break; /* not reached */
+ /* page is already in the swap cache, no need to decompress */
+ break;
case ZSWAP_SWAPCACHE_NEW: /* page is locked */
/* decompress */
@@ -698,6 +719,26 @@ static int zswap_writeback_entries(struct zswap_tree *tree, int nr)
return freed_nr++;
}
+/*********************************
+* periodic writeback (pwb)
+**********************************/
+void zswap_pwb_work(struct work_struct *work)
+{
+ struct delayed_work *dwork;
+ struct zswap_tree *tree;
+
+ dwork = to_delayed_work(work);
+ tree = container_of(dwork, struct zswap_tree, pwb_work);
+
+ zswap_writeback_entries(tree, zswap_pwb_writeback_pages);
+
+ spin_lock(&tree->lock);
+ if (!list_empty(&tree->lru))
+ schedule_delayed_work(&tree->pwb_work,
+ msecs_to_jiffies(MSEC_PER_SEC * zswap_pwb_delay_secs));
+ spin_unlock(&tree->lock);
+}
+
/*******************************************
* page pool for temporary compression result
********************************************/
@@ -854,8 +895,18 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
entry->handle = handle;
entry->length = dlen;
- /* map */
spin_lock(&tree->lock);
+
+ if (RB_EMPTY_ROOT(&tree->rbroot))
+ /* schedule delayed periodic writeback work */
+ schedule_delayed_work(&tree->pwb_work,
+ msecs_to_jiffies(MSEC_PER_SEC * zswap_pwb_idle_secs));
+ else
+ /* update delay on already scheduled delayed work */
+ mod_delayed_work(system_wq, &tree->pwb_work,
+ msecs_to_jiffies(MSEC_PER_SEC * zswap_pwb_idle_secs));
+
+ /* map */
do {
ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
if (ret == -EEXIST) {
@@ -1001,6 +1052,7 @@ static void zswap_frontswap_invalidate_area(unsigned type)
* If post-order traversal code is ever added to the rbtree
* implementation, it should be used here.
*/
+ cancel_delayed_work_sync(&tree->pwb_work);
while ((node = rb_first(&tree->rbroot))) {
entry = rb_entry(node, struct zswap_entry, rbnode);
rb_erase(&entry->rbnode, &tree->rbroot);
@@ -1027,6 +1079,7 @@ static void zswap_frontswap_init(unsigned type)
INIT_LIST_HEAD(&tree->lru);
spin_lock_init(&tree->lock);
tree->type = type;
+ INIT_DELAYED_WORK(&tree->pwb_work, zswap_pwb_work);
zswap_trees[type] = tree;
return;
--
1.7.9.5
--
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